It is known that electrochemical cells comprise two electrodes of opposite polarity with a separator being placed between them. The operation of alkaline electrochemical cells is based on oxidation-reduction reactions in the electrodes. The electrochemically active surface area of an electrode depends on the area that is wetted by the electrolyte. If the electrode is insufficiently wetted, then the active area is reduced, thereby increasing current density locally and thus reducing charged capacity. To obtain good performance as a storage cell, it is necessary for the electrodes to be thoroughly irrigated by the electrolyte.
Unfortunately, the negative electrodes that are usually used in alkaline cells are insufficiently hydrophilic, and this applies in particular not only to negative electrodes based on a hydridable metal but also to the negative electrodes of NiCd storage cells. In addition, the drying out of negative electrodes is accentuated by corrosion of the electrodes, leading to a "passivation" layer being formed thereon which absorbs a portion of the electrolyte.
Various techniques are known for increasing the hydrophilic nature of electrodes based on hydridable metal. A hydrophilic agent is generally added to the active material of the electrode.
For example, it is known to incorporate a hydrophilic polymer in the active material of the electrode. Nevertheless, that technique is no better than temporary since the polymer ends up by degrading in alkaline electrolyte and the negative electrode then loses its hydrophilic properties.
Document JP 0622 38 22 discloses the use of polyolefin hydrophilic fibers incorporated in said paste. The electrode is made more hydrophilic, but it is still not nearly hydrophilic enough. In addition, the resulting electrode is very friable when cut.